1. Field of the Invention
The invention relates generally to physiological monitoring devices and, more particularly, to tissue monitoring devices and methods for detecting harmful conditions including conditions that occur during intravascular infusion.
2. Relevant Background
An infusion system is commonly used to infuse a fluid into a patient's vascular system. Intravenous (IV) therapy is sometimes necessary for patient treatment and is generally considered a safe procedure. IV therapy is administered to approximately 80% of hospitalized patients in the United States. Some form of IV complication develops in nearly a third of patients receiving IV therapy. Most complications do not progress to more serious problems, but cases with further complications of IV failure are difficult to predict.
Several complications may arise from the infusion process including extravasation, tissue necrosis, infiltration, phlebitis, venous inflammation, and others. These complications can result in prolonged hospitalization, infections, patient discomfort, patient disfigurement, nerve damage, and additional medical complications and expense. Phlebitis is the largest cause of intravascular infusion morbidity. Infiltration and extravasation follow only phlebitis as IV morbidity causes.
When complications of infiltration, extravasation, phlebitis, or blood clots occur, the standard of care requires prompt removal of the IV to minimize further complications since continued pumping of infusate exacerbates the complications. Immediate detection of complications and termination of infusion reduces the possibility and damage of further complications. IV complications can cause failure to infuse a needed drug or fluid and lead to inadequate or sub-optimal therapeutic drug levels and hypo-volemia. Fluids that would lead to patient recovery may fail to reach the appropriate organs or tissue. Under life-threatening conditions or where infusion is life-sustaining, a patient's failure to receive fluids can be lethal. IV failure compromises patient safety.
Infiltration is the inadvertent administration of solution into surrounding tissue. Extravasation is the inadvertent administration of a solution that is capable of causing tissue necrosis when the material escapes or is infused outside the desired vascular pathway.
Extravasation sometimes results when an injection fluid, for example a contrast medium, is injected into a blood vessel. Extravasation is the accidental infusion of injection fluid into tissue surrounding a blood vessel rather than into the intended blood vessel. Various causes of complications that may occur with intravenous infusions include fragile vasculature, valve disease, inappropriate needle placement, infusion needle dislodgement of the cannula or needle delivering the fluid, microdilation of veins due to infusate chemical properties causing the material to leak from the vein dislodgement from the vessel due to patient movement, or infusion needle piercing through the vessel wall also due to patient movement. IV complication risk increases for elderly persons, children, cancer patients, and immuno-compromised patients.
Patients under therapy with vesicant drugs including chemotherapy, infusion of highly osmotic solutions, or high acid or low base solutions have risk of tissue necrosis if fluids are infused outside the vascular pathway. Examples infused agents include total parenteral nutrients, chemotherapeutic alkalating drugs, alkaline solutions, vasopressors (for example, Total Parenteral Nutrition (TPN)), antibiotics, hypertonic acids, KCl, and others. Many routinely-used antibiotics and medications are capable of causing extravasations and tissue necrosis. Antineoplastics can cause severe and widespread tissue necrosis if extravasation occurs. Chemotherapeutic agents are highly toxic IV drugs. Several drugs for emergency use have a well-documented high incidence of tissue damage. For example, administration of essential vasopressor drug dopamine in life-threatening or life-sustaining situations has a documented incidence of 68% tissue necrosis or extravasation at the IV infusion site. Caretakers cannot anticipate which complication will progress including necrosis to muscle.
Complications that may occur can cause serious patient injury by tissue trauma and toxicity of injection fluid. For example some injection fluids such as contrast media or chemotherapy drugs can be toxic to tissue if undiluted by blood flow. As a consequence, extravasation should be detected as early as possible and injection immediately discontinued upon detection.
In infiltration and extravasation, a condition occurs in which infused fluid enters extravascular tissue rather than the blood stream occurring, for example, when an infusion needle is not fully inserted to the interior of a blood vessel. Infiltrating fluid is infused into interstitial spaces between tissue layers, preventing proper intravenous drug administration and possibly resulting in toxic or caustic effects of direct contact of infused fluids with body tissues.
Infiltration and extravasation complications are costly and compromise patient outcome. Complications include pain and prolonged discomfort that may last for months, prolonged healing, ischemic necrosis due to vasoconstriction, opportunistic infections and septicemia, ulceration, cosmetic and physical disfigurement, and direct cellular toxicity for antineoplastic agents. Other complications include skin grafting, flaps, and surgical debridements, sometimes multiple. Further complications are compartment syndrome, arteriolar compression, vascular spasm, nerve damage (sometimes permanent), muscular necrosis, functional muscular changes, functional loss of extremities, amputation, reflex sympathetic dystrophy, and chronic pain syndrome.
Infiltration and extravasation can cause catheter-related bloodstream infection, including sepsis. An estimated 200,000 to 400,000 incidences of catheter-related infections occur annually, resulting in approximately 62,500 deaths, 3.5 million additional hospital days for treatment, and adds about $3.5 billion to the annual healthcare cost. Estimates of individual costs vary. A catheter-related bloodstream infection may cost $6,000 to $10,000 per incidence, and increase the hospital stay by up to 22 days.
Additional costs can be incurred. Additional medications may need to be injected to dilute or neutralize the effect of toxic drugs once tissue necrosis has begun to decrease the caustic reaction and reduce tissue damage. Surgical removal of the necrotic tissue may be required. Caretaker time, and therefore costs, increase since the extremities typically need to be elevated to improve venous return, warm and cool packs are applied, psychological comfort and pain medications given, and severity of the complication is monitored. A septic infection may cause a serious infection such as an infection in the heart.
Other conditions that result from improper supply of fluid to a patient in intravenous therapy include venous inflammation and phlebitis, swelling at the infusion site. Phlebitis complications include inflammation or thrombophlebitis that occurs with about 10% of all infusions. If phlebitis continues as the duration of infusion continues, the duration of the complication also increases. Phlebitis predisposes a patient to local and systemic infection. Phlebitis often results in a complication of infection resulting from use of intravenous lines. Underlying phlebitis increases the risk of infection by an estimated twenty times with estimated costs of IV infections between $4000 and $6000 per occurrence. When phlebitis is allowed to continue, the vein becomes hard, tortuous, tender, and painful for the patient. The painful condition can persist indefinitely, incapacitates the patient, and may destroy the vein for future use. Early assessment of complication and quick response can reduce or eliminate damage and save the vein for future use.
Another possible complication is blood clotting. IV needles and cannulas can become occluded with blood clots. As an occlusion intensifies, mechanical failure of the infusion can occur. Prescribed therapy cannot be administered if the catheter is occluded and multiple other complications can result, such as pulmonary embolism. Complications may progress, forming a thrombus and causing thrombophlebitis, or catheter-associated infections or bactermias.
Tissue necrosis may result when some of the infused materials are vesicant or other materials are infused outside the vascular pathway.
The current methods for detecting phlebitis, necrosis, infiltration or extravasation in a medical surgical patient undergoing therapeutic infusion are visual inspection and notification of pain by the patient. A caretaker visually inspects the intravascular insertion site or affected body parts for swelling, tenderness, discoloration. Otherwise, the caretaker requests or receives notification of pain by the patient but generally when tissue damage has begun.
Another problem that occurs with infusion is that the patient normally does not eat so that vital electrolytes can be lacking, a condition that is exacerbated by the patient's illness. One critical electrolyte is potassium. Medical protocols exist to replace needed potassium, but the level of replacement is difficult to determine. Low or high levels of potassium can lead to cardiac irritability and other complications. Electrolyte levels are commonly determined by electrochemistry testing, usually by blood draws, a painful procedure that commonly involves time delays for analysis.
What are needed are safe, reliable devices and methods that supply information on patient status of the presence or absence of IV complications. What are further needed are devices and methods that notify a caretaker of the occurrence of infiltration, extravasation, phlebitis, blood clots, and electrolyte levels with sufficient quickness to reduce or eliminate tissue damage, patient discomfort, and additional complications and associated costs.